Safety switch for airplanes



Nov. 23, 1948.

A. E. BAAK SAFETY SWITCH FOR AIRPLANES 5 Sheets-Sheet 1 Filed D80. 2,1942 3m eutor #13 577 ,5. 5/917.

Gttorngg A. E. BAAK 2,454,423

SAFETY SWITCH FOR AIRPLANES I 5 Sheets-Sheet 2 Nov. 23, 1948.

Filed Dec. 2; 1942 NOV. 23, 1948. BAAK 2,454,423

SAFETY SWITCH FOR AIRPLANES Filed D80. 2, 1942 5 Sheets-Sheet 3 w /4/ w#9 4g 4 I f 8L l i 12% w l O O I 3/ mg OE/ a/ m" (Ittorneg Nov. 23,1948. A E. BAAK SAFETY SWITCH'FOR AIRPLANES Filed Ded. 2,1942 5Sheets-Sheet 4 Littorucg Nov. 23, 1948. A. a BAAK SAFETY SIITCH FORAIRPLANES 5 Sheets-Sheet 5 Filed Dec. 2, 1942 WQ I...

Gttomeg Patented Nov. 23, 1948 SAFETY swrrcn FOR Ami-Lanes Albert E.Bank, Los Angeles, Calif.; asaignor to Minneapolis-Honeywell RegulatorCompany, Minneapolis, Minn, a corporation of Delaware ApplicationDecember 2, 1942, Serial No. 467,597

24 Claims. (01. 200-815) My invention relates to aircraft instruments,and more particularly to an instrument for indicating unsafe flightconditions of the plane.

During the training of aircraft pilots in blind flying, it is customaryto provide a hood-like cover which comes down over the cockpit of theplane so as to close off the vision of the pilot. simulating therebyactual flying conditions which the pilot may encounter and requiring thepilot to maneuver entirely during such flight by the aircraft indicatinginstruments.

During suchpractice maneuvering in blind flying, an inexperienced pilotmay well go into a. stall or dive without his detection of suchcondition until too late to prevent destruction of-the plane andoccupants, unless some means is provided for forcibly warning the pilotof the impending danger.

Further during such practice flight, it is quite possible for a pilot,if reckless or inexperienced, to literally fly the wings off the planeupon excessive speed by increasing the load on the wings beyond a saferange and causing the wings under extreme force to be actually torn fromthe plane.

It is an object of my invention, therefore, to provide an air speedswitch adapted particularly for use as a safety control for breakingupon such impending danger the circuit of a flying hood control. Theflying hood control circuit may be of a type such as disclosed in theco-pending application of Willis H. Gille, Serial No. 460,522, filedOctober 2, 1942, now Patent No. 2,420,946, granted May 20, 1947.

Another object of my invention is to provide a switch adapted to causeactuation of any suitable type of signal device upon the aerodynamicconditions of the plane approaching a predetermined unsafe condition.

Another object of my invention is to provide a novel control switchwhereby an aircraft pilot may be warned upon the plane exceeding apredetermined safe maximum speed and upon the speed of the planedecreasing below a predetermined safe minimum speed.

Another object is to provide a single aircraft speed responsive devicefor actuating two switches, and separate means for independentlymanually adjusting a measured force which the aircraft speed responsivedevice must offset to actuate each switch.

Another object of my invention is to make these adjustments simple andreadily accessible and to provide scales wherein each limit of air speedmay be separately read.

A further object is to provide in an aircraft instrument, a floatinglever which is operatively engaged at a mid point by an aircraft speedresponsive device and to oppose movement of the lever by adiustablespring means connected to opposite ends of the lever and to provideelectrical contacts positioned at opposite ends of the lever in such amanner as to break a circuit upon a variance in the force applied by theaircraft speed responsive device above a predetermined maximum force orbelow a predetermined minimum force.

Another object is to provide adjustable means for varying the springrate of the aforesaid spring means for the more accurate calibration ofthe instrument to the air speeds desired.

A further object is to provide in combination with an aerodynamicpressure responsive switch means, an acceleration responsive means,arranged so that upon-changes in the velocity of the plane the forcesdeveloped through the inertia of the parts of the switch mechanism willbe balanced so as to eliminate the accidental opening or closing of theswitch means which might otherwise result from the inertia thereof.

Other objects and advantages of this invention are set forth in thefollowing description, taken with the accompanying drawing, and thenovel features thereof are pointed out in the appended claims. Thedisclosure, however, is illustrative only and I may make changes indetails, especially in matters of shape, size and arrangement of partswithin the principles of the invention, to the full extent indicated bythe broad, general meaning of the terms in which the appended claims areexpressed.

In the accompanying drawing wherein like reference characters indicatecorresponding parts of the various figures,

Figure 1 isa plan view of one embodiment of my invention; Y

Figure 2 is an enlarged sectional view of Figure 1 taken along the line2-2 and looking in the direction of the arrows;

Figure 3 is an enlarged sectional view of Figure 1 taken along the line3-3 and looking in the direction of the arrows;

Figure 4 is a fragmentary sectional view taken along the line 4-4 ofFigure 3;

Figure 5 is a diagrammatic view illustrating my invention;

, Figure 7 is an enlarged plan view of Figure 6 with the top removed'andillustrating diagrammatically the manner in which the switch mechanismmay be connected into a control circuit;

Figure 8 is a sectional view of Figure 7, with the cover in place, takenalong the line 88 looking in the direction of the arrows and with aportion of the spring adjustment stem broken away;

Figure 9 is a top plan view of a third form of my invention;

Figure 10 is an enlarged plan view of Figure 9 with the cover brokenaway and showing the aisaeas relative position oi the annular springadjustment cams in dotted lines;

Figure 11 is a sectional view of Figure with the cover in place takenalong the line HH Having now particular reference to the first form ofmy invention illustrated in Figure 1, there is shown in Figure 2 andindicated generally by the numeral I, a casing or housing in which ispositioned the operating mechanism. As shown in Figure 2, there isaflixed to an open end of the casing I by attachment screws 2, a gasket3, an attachment plate 4, a second gasket 5, a sealing plate 6, and ascale plate]. The purpose of these structures will appear in more detailhereinafter. Projecting from the casing lare the ears or flanges 8, bymeans of which the instrument may be attached to the aircraft instrumentboard by suitable screws disposed in apertures 9 formed in the ears 8 asshown in Figure 1.

Provided in the supporting plate 3 as shown in Figure 3 are circularopenings ill and M in which are provided annular collars l2 and it.Afiixed to the annular collars l2 and it are the actuating or controlbellows it and t5, respectively. The collars l2 and it are sealed tothe' supporting plate 4 in any suitable manner and thereby effectivelyseal the interior oi the actuating bellows i4 and 65, respectively, fromthe interior portion of the casing l.

There are further provided in the top plate ii circular openings to andill concentric with the openings ID and M, respectively. Disposedrespectively in the openings it and ill in sealing relation are platemembers it and iii amazed in sealing relation to the top plate 5.Attached to the plates in and iii are the sealing bellows 2E9 and M,respectively. The said bellows 2@ and Eli are disposed concentrically inspaced relation within the actuating bellows iii and 05, respectively,as shown in Figure 3. Formed at the lower end of the sealing bellows 2tand 28 are the downwardly projecting annular flange portions 22 andrespectively. Slidably disposed within the sealing bellows 2t and 2H andfas-' tened thereto at the flanges 22 and are the partly perforatedinternally threaded block or nut like portions 2:? and 25, respectively.Screwthreadedly engaged in the block or nut like portions 2 and 25, arethe shafts or actuating screws 26 and 27, respectively. By turning thescrews 26 and ill the block portions 243 and 25 screw-threadedly engagedthereon may be adjusted up or down, thereby adjusting the movement ofthe sealing bellows 2t and 2t, respectively, for a purpose which will beexplained.

. The adjustment screws 26 and 27 are journalled at 233 and 29,respectively, in the plates iii and I9 and project out of the casing lin the form of screw shafts 3t and 311. Screw=threadedly engaged on thescrew shafts 3t and ti are bushings 32 and 33,, respectively. Mounted onthe bushings 32 and 33 are the adjustment knobs M and 35 which arefixedly fastened to the bushings engaged on the screw shaft by thefastening or retention screws 36 and 31, respectively. The adjustmentknobs 34 and 35 have provided the radially projecting annular flanges 93and 94 in which are formed a plurality of slots 95 and 86, respectively.Projecting through the slots 95 and 98 and screw-threadedly engaged inplates 18 and 39 are'the adjustment screws 42 and 43 for adiustablyfastening to the flanges 83 and 94 the plates 38 and 39. The plates 38and 39 have formed integral therewith the indicator pointers 40 and 4|;respectively. For calibration purposes the screws 42 and 43 may belongitudinally adjusted in the slots 85 and 86 so as to convenientlycalibrate the pointers 40 and 4| with respect to scale markings 44 and45 formed in the scale plate I as shown in Figure l.

The indicator pointers 40 and U are adapted upon adjustment of the knobs34 and 35 to cooperate with the scale markings 44 and 45 so as toindicate the airspeed for which such adiustment is made.

Mounted at the free ends of sealing bellows 20 and 2|, respectively, arethe helical springs 46 and 41 engaging at one end the sealing bellows 20and 2t and at the opposite end the inner surface of the movable end orbellows l4 and I5, respectively. It will thus be seen that by varyingthe adjustment oi the knobs 34 and 35 the position of screw-threadedblocks 24 and 25 will correspondingly be adjusted and accordingly thecompression of the springs 46 and 4?. Thus, the compression acting uponthe actuating or control bellows M and l 5 may be readily adjusted.

As shown in Figure 3, there is mounted on the inner surface of thecasing l adjacent the free ends of the bellows it and a resilient sprinblade 48. The resilient spring blade 48 is clamped at a pointintermediate the opposite ends thereof between two insulation members itand 5d. The insulation members it and Ed are in turn fastened by thebolts 58 to the lower inner surface of the housing ll.

Fastened at one end of the blade in by a button or rivet 52 is adownwardly bent arm. 53. Mounted at the free end at the arm 53 is a contact 5s adapted to cooperate with a second contact tit formed on an armThe arm 56 is mounted on the lower inner surface of the casing l and isinsulated from the casing i by insulation member Mounted on the oppositeend of the blade to is a contact button adapted to cooperate with asecond contact Mounted at the lower underside of the actuating bellows tl and iii, are the attachment members and lit in which are securedinsulation members 62 and respectively, as shown in Figure 3. Theinsulation members [32 and are adapted to bear against the buttons andto, re spectively, previously mentioned, mounted at op posite ends ofthe spring blade It will be read ily seen from Figure 3 that theactuating bellows it under compression of the spring 46 willtend to beardown upon the button 52 through the insulation member 62 and therebytend to open the switch at the contact points 55 and 5d. Further, itwill be seen that the actuating bellows it under compression of springit will tend to bear down through the insulation member 63 upon button5t and close the switch formed by the contacts to and 59.

AS shown in Figure 2, the instrument is Provided with a connection 84 towhich the dynamic pressure line of a standard Pitot tube is connected.The connection 54 leads through a channel 55 into the interior of thecasing i so that such dynamic pressure will tend to cause thecontraction of the bellows l4 and i5. A second connection is providedindicated by the numeral 85 to which the static pressure line of astandard Pitot tube is connected. Such connection leads through achannel 81 drilled in the casing I, as indicated in Figure 2, through anorifice 88-formed in the gasket 3 and a second oriflce 68 formed in thesupporting plate 4. The orifice 58 opens in turn into a space formedbetween supporting plate 4 and the sealing plate 6 which are spacedapart in sealing relation by the gasket 5. The static pressure isconducted through the space 10 directly into the interior of the bellowsl4 and I5 through the spaces II and 12 provided between the bellows l4and i5 and the sealing bellows and 2i, respectively, as shown in Figure3. It will thus be seen that the static pressure within the bellows l4and [5 will tend to augment the expansive force of the helical springs48 and 41,

respectively, and counteract the dynamic force exerting pressure uponthe exterior surface of the bellows l4 and 15, as previously explained.Thus, as the difference between the static and the dynamic pressuredecreases the bellows I4 will tend to expand causing the contacts 54 and55 to break upon a diflerential in pressure below a predetermined value.Further, it will be seen that as the diflerence in pressure between thestatic and dynamic pressure increases, the bellows l5 will tend tocontract causing the contacts 58and 58 to break upon a diflerential inpressure above a predetermined value.

As shown in Figure 3, the contact member 59 is mounted in a pin I8 whichforms one terminal for the inlet circuit of the control switch 48. Therei'urther is connected to the contact 55 through the arm 55, anelectrical conductor 14 which has the opposite end thereof connected toa pin 15 shown in Figures 4 and 5. As shown in Figure 2, the springblade 48 has a projecting part 15 to which is connected an electricalconductor 11 which has the opposite end thereof connected to a pin 18,as shown in Figures 3 and 5. The pins 13, I5 and 18 are positioned in asuitable socket l3 and the said pins are adapted to engage correspondingcontacts of a plug of conventional type. not shown. As showndiagrammatically in Figure 5, the electrical conductor 80 leads to theterminal 13 from a suitable source of electrical energy indicated bynumeral 8 I The opposite terminal of the source of electrical energy 8|is connected through a conductor 89 to two conductors 84 and 81 leadingrespectively to a terminal of separate electrical control devicesindicated generally by the numerals 83 and 86. A conductor 82 leads fromthe terminal 18 to the opposite terminal of the control device 83 whichis shown here as an electromagnet. The electromagnet 83 controls aspring switch arm 400 which upon enengization of the electromagnet 83biases the arm 400 so as to open the contacts 40l and 402. But upondeenergization oi the electromagnet 83, as upon the opening of thecircuit at the contacts 58 and 59, the spring switch am 400 is biased toan opposite position by the tension of the spring arm 400 closing thecontacts 40! and 402. Upon closing the contacts 4M and 402 an electriccurrent flows from a suitable source of energy indicated by numeral 404through a conduit 405, switch arm 400, contacts 40] and 402,

conductor 486, indicator 481 which obviously ml! be a light, bell, orother indicating device and returns to the source 0! electric energythrough a conductor 408. It will be noted that the indicator 401 will beactuated only upon the openin of contacts 58 and 58 and will not beactuated upon the opening of contacts 54 and 55. Further an electricalconductor leads from the terminal 15 to the other terminal of theelectrical control 86 which may operate a flying hood release latch of atype such as described in detail in the copending application of WillisH. Gille, Serial No. 460,522, filed October 2, 1942, and shown herein inFi ure 14, or the same may be any other suitable means or indicatingdevice. It will be seen, however, that the indicating device or releasemagnet oi. the control device 88 of Figure 14 will be actuated upon theopening of either contacts 54 and 55 or contacts 58 and 58 causing theopening of the flying hood as explained in detail in the atorenotedapplication of Willis H. Gille.

From the circuits shown in Figure 5, it will .be readily seen that innormal operation the switch contacts 58 and 58 will be closed as willthe switch contacts 55 and 54, in which case the circuits to.devices 83and 88 will be closed through the switch arm 48. Upon an increase indynamic pressure above a predetermined Point, the bellows l5 willcontract causing the contacts 58 and 58 to open under tension of thespring blade 48, thus opening the circuit to both thecontrol devices 83and 85, in which case should the device 86 control the flying hoodrelease latch as noted, the flying hood will open and further theindicating alarm or device 83 will be actuated. However, upon a decreasein the dynamic pressure below a predetermined point, the bellows l4 willtend to expand, thereby causing the switch contacts 55 and 54 to openagainst the tension of spring arm 48 and thus open only the circuit tothe control device 86, which if the same controls a flying hood such asnoted will cause the flying hood to open. It will be seen that underthis arrangement the flying hood will be released upon an increase indynamic pressure above a predetermined point and also upon a decrease indynamic pressure below a predetermined point,

and that furthermore through the indicating device operated by thecontrol device 83 the operator or pilot will be immediately advised asto whether such a release is due to aerodynamic conditions above orbelow the predetermined limits. Thus the pilot may promptly maneuver theplane so as to overcome such conditions without for example, increasingthe speed of the plane, when it should be decreased, or decreasing thespeed when it should be increased,

The helical springs 45 and 41 are so calibrated with respect to. theinstrument that by adjusting the knob 34 and accordingly the indicatorpointer 40 upon the scale 44, the lower limits at which the contacts 54and 55 will break or the minimum air speed at which the contacts 54 andthe control contacts 58 and 58 will remain closed I may be convenientlyadjusted. The indicator pointer 4| thus will read on the scale 45 themaximum speed limit beyond which the control circuit will be opened andsuitable indicating means energized.

in the bottom wall of easing till.

a e-sense In order to lock the adjustment knobs 8K and 35 in adjustedposition, I have provided a con= venient clamping means includingclamping plates indicated by numerals 88 and 92. The clamping plates 88and 92 are adjustably mounted on pins 89 and 90 which are affixed to thetop plate 6 and project through suitable apertures formed in theclamping plates 88 and 92. A bolt 3I is further provided projectingthrough a suitable aperture in the plate 88 and threadedly engaged inplate 92 so as to adjustably clamp between'the same the annular flanges83 and 94 together with the indicator plates 38 and '39. Thus throughadjustment of the bolt 9| the knobs 34 and 35 may be afllxed in adjustedposition released for further adjustment.

A second modified form of my invention is illustrated in Figures 6, 7,and 8 wherein I have provided a casing indicated by numeral IIlI formedof suitable insulating material. Projecting from the casing IOI are earsI82 whereby the instrument may be positioned in the wing of the plane orin the cabin or instrument board as may be desired. The casing IOI isprovided with a connection I02 to which the static pressure line of astandard Pitot tube is connected. As shown in Figure 8, a channel I03leads from the connection. I02 into the interior of the casing I (II. Asecond connection 34 is provided to which the dynamic pressure line ofthe Pitot tube is connected.

The lower inner wall of the casing It has formed therein an annularrecess 506 in which there is in turn formed a smaller circular recessI05, The dynamic pressure connection M4 leads into the recess Hi5.Extending across the recess I06 is a circular diaphragm lull fastened tothe inner surface of the lower wall of the casing Hill by the fasteningplate Hill which is in turn fastened by the attachment screws I539.Fastening screws I09 are disposed through suitable aper-= tures formedin the fastening plate Hi8 and diaphragm Ill? and are screw-threadeollyengaged As best shown in Figure 8, the fastening plate W8 has providedtherein an annular recess l ill corresponding to the oppositelypositioned recess tilt formed in the bottom wall of the casing iilfi.Mounted on the diaphragm it'll are a pair of concentric circular disksiii and M2 positioned at opposite sides of the diaphragm Ililll andsuitably fastened thereto by rivets iii A post Hi l is centrallyafic'ured to the disk i it by a screw M disposed in a suitable centralaperture formed in the dish Ml, diaphragm HM, and disk M2. The screw M5projects upwardly through the said disks and dia phragm andscrew-threadedly engages the loot tom of the post ll l so as to securelyfasten post HM to the disk M2. The post i Mi projects unwardly through asuitable aperture formed in the fastening plate M38, as shown in Figures7 and 8. An adjustable bolt fill is screw-threadedly en= gaged in theupper end of the post M5. The adjustable bolt ll'l has formed at theupper end thereof a plate Mt on which is mounted a knifeedge bearing M9which seats in a depression Mil formed in a lever or switch arm 02 l.

The lever iZl has formed on opposite ends thereof the depressions i222and 1123 in which are disposed respectively links i226 and U25.Supported by the casing till is a knife-edge Md about which a bell-cranklever i2? is adapted to turn. Provided in one end of the bell-cranklever 92? is a depression 928 in which is positioned the lower end orthe link lit. In the opposite end to the stem I145.

of the bell-crank lever I21 is a depression I29. Positioned at one endin the depression I28 is a link l3t which has the opposite end thereofsecured to a tension spring I31. posite end of the tension spring I 3|is a nut I32 threaded on a stem I33 of a screw I34. The stem of thescrew I34 projects through a suitable aperture formed in the casingIilI. A gasket or washer I35 surrounds the stem of the screw and ismounted adjacent to the head of the screw I34. A spring I36 surroundsthe stem I33 and acts against the inner wall of the casing IM and a bossI31 secured to the stem I33 so as to hold the head of the screw I34within an annular depresslon formed in the outer surface of the easing I0| against the gasket I35 under tension at all times. The gasket I35 isso arranged as to seal the aperture formed in the casing IIII throughwhich the stem of the screw I34 is disposed.

A knife-edge bearing I38 is mounted on the casing IOI so as to support abell-crank lever I39 which is adapted to rotate about the knife edge B8.A depression I40 is formed at one end of the bell-crank lever I39 andhas positioned therein the lower end of the link I25 previouslydescribed. The opposite end of the bell-crank lever I39 has formedtherein a depression MI in which is received a link I42. The link I42has fastened at the other end thereof a tension spring I43. At theopposite end of the tension spring I43 is fastened a nut I44screw-threadedly engaged on a stem E45 of a screw MS. The stem I45-projects through a suitable aperture formed in the casing wall Hill. Agasket or washer I47 surrounds the stem of the screw and is mountedadjacent to the head of the screw I46 which is disposed in an annulardepression formed in the outer surface of the casing wall It l. Acompression spring I48 surrounds the stem H45 of the screw I46 and ispositioned between the inner surface of the casing ml and a boss M9which is securely affixed Thus the spring I48 will hold the screw head.I58 and gasket Ml securely against the casing Hill and thereby seal theaperture formed in the casing it! for the passage of the stem M5 ofscrew M3.

From the foregoing structure it will be seen that the bell-crank leversi271 and 639 will exert a tension on the opposite ends of the arm Iiiwhich is pivotally mounted in turn at the depression ll Ed on the knifeedge bearing Ill'il.

An electrical contact indicated by the numeral 11559 is mounted at oneend of the lever 82H and is adapted to cooperate with a second contactHit. The second contact I156 is positioned on a bracket I152 affixed tothe side wall of the casing Hit by a screw fl53. The screw I353 projectsthroughthe wall of the casing Mill through a suitable aperture formedtherein and is screwthreadedly engaged at the opposite end by a nut 55i. Screw I153 forms one terminal of the'switch circuit of the saidinstrument. A second contact I 55 is mounted at the opposite end of thelever 823i and at the other or under side of said lever. The contact 6is adapted to cooperate with a contact 953 mounted on a bracket H53. Thebracket it? is attached to the opposite wall of the casing Mil from thatof the bracket i552 and is attached to the said wall of the casing ill!by a bolt I58 which projects through the wall of the casing Hill and isscrew-threadedly engaged at the outer side by nuts I 59. The bolt H58forms the instrument.

Secured to the op-- It will be readily seen that the contact III formedon the bracket I52 serves as a stop limiting the upwardcounter-clockwise pivotal movement of the lever I-2I. Further, thecontact I56 mounted on the bracket I51 limits the downwardcounter-clockwise pivotal movement of the lever I2I. A stop I66 isfurther provided to limit the downward clockwise pivotal movement ofthat end of the lever I2I at which the contact I56 is mounted.

It will be readily seen that upon an increase in the differentialpressure exerted at the diaphragm I61 above the tension exerted by thespring I3I on the lever I2I will cause the contacts I55 and I56 tobreak. Further, upon a decrease in the diil'erential pressure at thediaphragm I61 below that exerted by,the spring I43 upon the lever I2Iwill result in a break between the contacts I-5I and I56 due to thedownward pivotal movement of the lever I2I under tension of the springI43. It will thus be seen that I have provided a novel arrangementwhereby upon a predetermined increase or decrease in pressure above orbelow a predetermined maximum and minimum pressure, a break in thecircuit controlled by the switch lever III will be readily effected.

As shown in Figures 7 and 8, the screw heads I34 and I46 have beensuitably arranged so that the same may be readily adjusted for varyingthe tension of the springs I and I43, respectively. Further, in orderthat the adjustment of the springs I3I and I43 may be readilyascertained there are mounted on the nuts I32 and I44, re,- spectively,arms I 6| and I62. The arm I6I projects upwardly into a slot I 63 formedin a top plate I64 fastened to the casing IN by suitable screws I 65. Aglass I66 covers the slot I68 formed in the top plate I64 and providessuitable means whereby the position of the arm I6I may be readilyascertained. As shown in Figure 6, scale markings I 61 are providedadjacent to the edge of the slot I63 and are adapted to cooperate withthe arm I6I so as to indicate the air speed at which the spring I3I isadjusted for the breaking of the circuit controlled by the switch armI2I and the contacts I-55 and I56. It will thus be seen that by turningthe head of the screw I34, the tension of the spring I3I may be variedand the adjustment thereof indicated through the arm I6I on theindicating scale I61.

The arm I62 further projects upwardly into a slot I68 formed in the topplate I64, as best shown in Figure 6. A glass I66 covers the slot I68 sothat the position of the arm I62 may be readily determined. Anindicating scale I16 shown in Figure 6 is mounted adjacent to the edgeof the slot I68 and is adapted to cooperate withthe arm I62 forindicating the air speed at which the spring I43 is adjusted for causingthe opening of the circuit controlledby the arm I2I at the contacts I5Iand I56.

As will be readily seen from Figure 8, the

dynamic pressure present in the connection I64 will exert a force uponthe disk III tending to force the post II4 upwardly. However, the staticpressure entering through the connection I62 and channel I63 into theinterior of the easing I6I will exert a force through the opening I I6upon the disk I I2 which will tend to counteract the force exerted uponthe disk III by the dynamic pressure entering through theconnecticn'I64. The static pressure will be augmented in thiscounteracting effect by the tension of the springs I3I and I48 actingupon the bell-crank levers I21 and I33, respectively, upon the lever armI2I. Thus as the tension of the springs III and I43 is increased thedifferential between the presures exerted by the dynamic and staticpressures must necessarily be increased to balance the same. It willfurther be seen that if such diflerential pressure is greater than theadjusted tension of spring I43 and is further less than the adjustedtension ofspring I3I, the force exerted upon the arm I2I will move thecontact I56 into engagement with the contact I5I while the tension ofspring I3I will pivot the arm I2I at the opposite end so that contactI55 will engage contact I56. In this position, the control circuit willobviously be closed. Upon the speed of the plane increasing, however, toa point where such differential pressure exerts a force greater than thetension of spring I3I, the lever I2I will be pivoted upward with thecontacts 'I5I and I56 as the bearing point so as to overcome the tensionof spring I3I and open the contacts at the points I55 and I56. Moreover,should the speed of the plane decrease to such a point where thedifferential pressure will exert a force less than that for which springI43 is adjusted, the lever arm I 2| will move downwardly with thecontacts I55 and I56 as the bearing point and cause a break in thecontrol circuit at the contacts I56 and- I5I, the downward clockwisemovement of the lever arm I2I being limited by the stop I66, aspreviously described.

I have further provided in my control switch a novel means forpreventing the accidental -opening or closing of the switch mechanismdue to the effect of gravity thereon and the resulting inertia of theswitch mechanism mass upon acceleration or deceleration, or change inthe direction of flight of the plane as upon a sudden ascent or descentthereof. I have accordingly provided means for counter-balancing theforces exerted through the inertia of the switch mechanism mass inresponse to the aforesaid causes.

Thus vertically projecting from the knife edge bearing plate H8 is anarm ill from which projects laterally a plate I12. The plate I12supports one end of a compression spring I13 which is engagedat theopposite end by the switch lever I2I. The spring I13 serves to preventthe accidental displacement of the switch arm I2I from the knife edgebearing IIS. Afflxed to the upper surface of the plate I12 and centrallylocated thereon is the vertically projecting bifurcated arm I14.Pivotally connected between the bifurcations of the arm I14 by a pinI15, is an arm I16. Arm I16 has mounted at the free end thereof aweighted portion I11. Pivotally connected intermediate the weightedportion I11 and the pivotal connection I15 is a post I18 connected tothe arm I16 by a pin. I86. The post I18 has mounted at the lower end abase I16 which is affixed to the supporting plate I68.

The weight of the weighted portion I" is of sufilcient value so as tobalance the weight exerted on the opposite end of the arm I16 at the pinI15 by the switch mechanism parts. Thus if the acceleration of the planeis such that the inertia of the switch mechanism mass exerts a downwardforce upon the arm I16 at one end the inertia of the weighted portionI11 will exert a corresponding downward force at the other end of thearm I16 and thereby counter-balance the force exerted through theinertia of the switch mechanism mass. Likewise upon the inertia of theswitch mechanism mass being such as to exert an upward force the samewill correspondwill operate with extreme accuracy, unaflected by forcesexerted through the inertia of the switch I mechanism mass due tochanges in the velocity of the plane. Further such counter-balancingmechanism will substantially prevent the actuation of the mechanism bythe vibration of the plane. I

There is further'provided an electrical conducting strap I90'connectedat one end to a terminal or bolt ISI which projects through the casingIM and is screw-threadedly engaged at the outer side of the casing IOIby nuts I92. The opposite end of the strap I90 is fastened by the boltI09 to the plate I08 whereby the strapmay be electrically connected tothe switch arm or lever I2I through the post I18, pin I80, arm I15, pinI15, arm I14,

12 A second connection 2I0 is mounted on the plate 204 for connection ofthe dynamic pressure line of the Pitot tube.

The inner surface of the plate 204 has formed therein an annular recess2 in which there is provided a smaller annular recess 2I2. The dynamicpressure connection 2I0 leads into the recess 2I2. The diaphragm 200extends across the recess 2 and has mounted thereon a pair of concentriccircular disks 2I3 and 2I4 positioned at opposite sides of the diaphragm208 and suitably fastened thereto by rivets 2 I 5. Suitably fasarm "I,knife edge bearing plate II8, knife edge hearing I I9 and spring I13contacting the lever or switch arm I2 I. i

It will be seen from the diagram shown in Figure 7 that the latterswitch mechanism is readily adapted for controlling suitable controlcircuits such as the flying hood control circuit and the indicatorcontrol circuit previously described and explained with reference toFigure 5. The numerals shown in the circuit diagram of Figure 7 and theparts indicated thereby correspond to v those shown with reference toFigure 5.

Moreover it will be readily apparent that by adjusting the tension ofspring ten for the predetermined maximum air speed desired as indicatedthrough the arm Mil and further adjusting the tension of spring M3 forthe predetermined minimum air speed desired. as indicated through thearm I62, the flying hood holding circuit controlled by the arm I23 willconveniently open upon such predetermined maximum and minimumaerodynamic air speed conditions. Further,

such circuit will remain closed during air speed conditions between saidpredetermined minimum and maximum air speed conditions. Moreover thealarm or indicator light 407 will be energized only upon thedeenergization of the relay magnet 83 which will occur only upon theopening of the switch contacts I55 and I 55 by the switch arm ii i upona predetermined maximum air speed condition. The energization of therelay magnet 83 being unaffected by the opening and closing of theswitch contacts I50 and I5I. Thus the pilot in control of the plane uponthe automatic release of the flying hood will be immediately advised asto the cause thereof and the nature of the impending danger, whether dueto the low or high speed of the plane.

A third modified form of my invention is illustrated in Figures 9, 10,11, 12 and 13. As best shown in Figures 10 and 11 I have provided acasing indicated by numeral 20I to which is fastened by the screws 202,the insulation plate memher 203 and the bottom plate member 204. The

into the interior of the casing 20 i tened to the upper plate 2 at acentral point therein is an actuating post 2I6. oppositely disposed tothe recess 2| I is a second annular recess 2 I 1 or equal size formed inthe plate 203. The diaphragm thus positioned between the plates 203 and204 is adapted to fluctuate within the space formed by the recesses 2I Iand 2" in response to the dynamic pressure introduced through theconnection 2I0., An annular opening 2I8 is further provided in the plate203 and the said opening 2I0 leads from the recess 2| 1 to the interiorof the casing 20I. Projecting through the opening 2I8 is the post 2 I 6which is spaced apart from the side walls of the said opening. It willthus be seen that the static pressure entering through the connection205 into the interior of the casing 20I through the channels 206 and 201respectively will act upon the diaphragm 208 through the disk 2I4 so asto tend to counteract the force of the dynamic pressure acting upon theopposite disk '2I3. Thus any resulting movement of the post 2 I6 willrepresent the difference between the static and dynamic pressuresrespectively,

Mounted on the insulation plate 203 within the casing 20I is a switchsupporting bracket 2I9 fastened by the screws 220 secured in the plate203 as shown in Figure 12. Projecting from the bracket plate 2I0 are theoppositely disposed bracket arms 22E and 222; Pivotally disposed betweenthe arms 22I and 222 is a switch bracket 223. Th switch bracket 223 hasprovided upwardly projecting arms 224 and 225. The arms 224 and 225 arepivotally connected to the respective arms 22I and 222 by the pins 226and 221.

Further projecting from the arms 224 and 225 are inwardly bent arms 228and 229 which are suitably apertured to receive the opposite ends 230and 23I of a hair pin shaped spring 232. As best shown in Figures 10,11, and 12 there is slidably mounted on the switch plate 223 anadjustment plate 233. The adjustment plate 233 has formed therein a slot234 in which is disposed an eccentric adjustment screw 235. Projectingfrom the plate 233 at one end and extending at a right angle thereto, isa supporting member 236, adjustably positioned intermediate the loopedend of the hair pin shaped spring 232 and the attachment end of the saidspring. By turning the eccentric screw 235 the position of thesupporting member 236 with respect to the spring 232 may be varied asdesired and the effective spring rate of the spring 232 therebyadjusted.

The adjustment plate 233 has provided at the opposite ends thereof theattachment screws 231 and 238 which, as best shown in Figure 10, aredisposed in the slots 239 and 240 formed in the switch plate 223. Uponadjusting the plate 233 to the position desired through the eccentricscrew 235 the plate may be fastened in such adjusted position bytightening the screws 231 and 238 in the respective slots 2'39 and 240.

The looped end of the hair pin shaped spring 232 rides upon theadjustable cam surface of an adjustment cam 24! whereby the tension ofthe hair pin shaped spring 232 may be conveniently athusted. The cam 2is fastened for the rotary adjustment on a shaft 242 which is channeledin the casing 23|. The shaft 242 has fastened at the opposite end by abolt 243 an adjustment kn'ob 244. The knob 244 has formed thereon theradially projecting annular flange 246 in which are formed slots 246.Adjustably positioned in the slots 246 are attachment screws 241 whichscrew-threadedly engage a plate 248 which has formed thereon a pointer249. For calibration purposes the screws 241 may be variably positionedwithin the slots 248 so as to adjustably position the pointer 249 withrespect to the knob 244. The indicator pointer 249 is adapted tocooperate with suitable scale markings 253 provided on a scale plate 25|for purposes that will be explained hereinafter. It will be readilyapparent that by adjusting the knob 244 the position of the surface ofthe earn 2 with respect to the hair pin shaped spring 232 may be variedand accordingly the tension ex erted by the biasing spring 232 adjusted.

A contact point 252 is mounted on the under side of the switch plate 223at the opposite side of the pivots 226 and 221 from the supportingmember 236. The contact point 252 is adapted to cooperate with a furthercontact point 253 as will appear. I

Further projecting from the switch arm 224 at the opposite side of thepivot 226 from the contact 252 is an actuating arm 254 having formedtherein a slot 255 for receiving a link 256. This link 253 is operablyconnected to the post 2|8 as will be explained.

At the opposite side of post 2l6 diagonally positioned with respect tothe switch bracket 2|9 is a second switch bracket 263 similarlyconstructed as the switch bracket 2|9 and attached to the 14 adjustedposition by tightening the fastening screws 213 and 213. A contact 233is mounted at the underside of the switch plate 284 at the same side ofthe pivots 261 and 263 as the supportin member 211. A

The looped end of the hair pin shaped spring 213, as indicated in Figure11, is adapted to ride along a cam surface provided on the adjustablecam 233. Cam 236 is fastened to an adjustment knob 231 similarlyconstructed to knob 244 previously described. The cam 285 may be rotatedby means of the knob 231 so as to adjustably position the hair .pinspring 213 for the adjustment of the tension thereof. The knob 281 hasprovided an indicator pointer 288 for cooperation with suitable scalemarkings 3| l.

Projecting from the switch arm 266 is an actuating arm 239 having formedtherein a slot 293 in which is held a link 29L Formed in the oppositeend of the post 2l6 from the diaphragm 238 is a depression 292 adaptedto receive a knife-edged pivot or hearing screw 294. The knife-edgebearing screw 294 is screwthreadedly engaged in an arm 295 at a pointintermediate the opposite ends thereof. The arm 285 has positioned atthe opposite ends thereof the downwardly projecting arms 296, and 291which have provided slots 238, and 299 forreceiving the links 29| and256, previously mentioned. Links 29| and 256 are positioned inrespective slots 293 and 299 at opposite sides of the pivot formed bythe knife-edge 294 in the slot 232. Thus the arm 295 will readilybalance the knife-edge screw 294, as indicated. The contact 233 mountedon the underside of the switch blade 264, as previously noted, isadapted to cooperate with a second contact 293 which is mounted on thestrap 333 fastened to' the plate 233 by the bolts 33L An electricalconductor 332 is in turn connected at one end to the strap 333 and atthe opposite end to the conductor 33 leading to one terminal of asuitable source of electrical energy indicated by the numeral 3| Thecontact 253, previously noted, is mounted on a strap 333 fastened to theplate 233 by the bolts 286. The strap 333 is in turn connected by aconductor 334 to conductor 85 which is connected to one terminal of asuitable indicating device or flying hood control circuit 86 such asillustrated in Figure 14 and previously noted.

Y The opposite terminal of the control circuit 86 vary the effectivespring rate of the hair pin shaped spring 213 there is slidably mountedon the switch plate 264 an adjustment plate 214. The adjustment plate214 has provided therein a slot 215 in which is suitably disposed aneccentric adjustment screw 216 wherebythe adjustment plate 214 may beslidably positioned. Mounted on the adjustment plate 214 at an endopposite from that in which the free ends of the hair pin shaped spring213 are secured to the switch plate is a supporting member 211 whichprojects upwardly at a right angle from the plate 214 and engages thehair pin shaped spring 213 intermediate the looped end and the attachedends thereof. It will thus be seen that by adjusting the position of thesupporting member 211-with respect to the hair pin shaped spring 213 theeffective spring rate of the hair pin shaped spring 213 may be readilyadjusted.

Screw-threadedly engaged in the adjustment plate 214 are fasteningscrews 218 and 219 which are slidably disposed in slots 28| and 282formed in the switch plate 264. Upon adjustment of the plate 214 theplate may be readily secured in such is connected through a groundconductor 81 to a grounded conductor 99 leading from the oppositeterminal of the source of electrical energy 8|. A conductor 335electrically connects the bracket H9 and the bracket 263 so that anelectrical connection between the brackets 2 I 9 and 263 and the switchbrackets 223 and 264 is assured. An electrical connection 336, Figures10 and 12, interconnects oppositely projecting parts of the arms HI and225, respectively, while an electrical connection 331, Figure 10,suitably interconnects upwardly projecting parts of the arms 265 and283, respectively.

It will thus be seen that upon the contacts 252 and 253 being inengaging position and the contacts 283 and 293 being in engagingposition, a closed circuit will result. Upon either of these contactsbeing broken the circuits will in turn by the numeral 308 which may beoperated in a manne described in the application of Willis H. Gille,erial' No. 460,522, filed October 2, 1942. Of course in piaceof the hoodrelease latch this circuit may obviously control any other suitableindicating or control device.

In operation, it will be seen that when the differential pressureexerted upon the post 266 or the airspeed of the plane exceeds apredetermined point, post 2l6 will move upward causing a clockwisepivotal movement of the lever 295 which will inv turn pivot through thlink 23f the switch arm 264 in a counter-clockwise direction breakingthe contact between the contact points 283 and 293. Thus upon apredetermined high airspeed the circuit controlling the hood releaselatch will be opened, thus causing the release of the hood upon apredetermined high airspeed.

Further, upon the differential pressure exerted upon the post 2H5decreasing below a predetermined point or the airspeed of the planedecreasing below a predetermined airspeed, the post 256 will tend tomove downwardly causing a downward pivotal movement of the arm 295 in aclockwise direction. This movement of the lever 295 will be transmittedthrough the link 256 to the switch arm 223 causing counter-clockwisemovement of the switch lever 223 which will in turn cause the opening ofthe circuit between the contacts 252 and 253. Thus the circuitcontrolling the hood release latch will be opened upon a predeterminedlow differential pressure or low airspeed of the plane.

The airspeed at which the respective switches will open the circuit willof course depend upon the tension exerted upon the switch arm 264 by thespring 213 and the tension exerted upon the switch arm 223 by the spring232. This tension may be conveniently adjusted through the respectiveadjustment knobs'28'l and 244, as previously explained. The respectivescale markings 3H and 250 are adapted for cooperation with theadjustment knobs and are calibrated so that the adjustment knobs may beadjusted for the airspeed desired.

In order that the airspeed condition causing the opening of the hood maybe readily determined, I have provided novel indicating means operatingupon the circuit opening the contacts 283 and 293 under high airspeedconditions. Connected to the connector 305 is a second electricalconductor 310 which leads to a conductor 82 for controlling a relayswitch magnet 83 such as shown in Figure 11. The electromagnet 03 isconnected through a grounded conductor 84 to the opposite terminal ofthe source of electrical energy indicated by numerals 8|. .Upon thecircult of the electromagnet 83 being closed, switch arm 400 is actuatedby the energized magnet 83 so as to open an indicator control circuitthrough contacts 4M and 402. Upon the circuit of electromagnet 03 beingopened, by the opening of the contacts 293 and 283, the spring arm 400is- 16 source 404 through the conductor 40!, arm 400, contacts 40l and402, connector 408 to the indicating lamp 401 and returning to thesource of electrical energy 404 through the conductor 400. It willthusbe seen-that upon the hood being released and the indicating lampbeing energized, the operator will immediately know that the cause ofsuch opening of the hood was due to an excessive speed of the plane.While if the hood should release and the indicating lamp not beenergized, the operator will accordingly know that the release of thehood was due to the fact that the plane was flying at an excessively lowspeed. Thus the air pilot will be enabled to immediately correct suchconditions without delay and thereby avoid possible disastrous results.

In order to prevent the foregoing switch mechanism from being actuatedby the inertia thereof or by the vibration of the plane during flight ofthe plane, I have provided means to counterbalance such effect. Suchmeans includes a counter-balancing lever 350 plvotally connectedintermediate the opposite ends thereof by a pin 35l to a fixed post 352.Post 352 is fastened by a bolt 353 to plate 203, as best shown in Figure13. The switch actuating post 2l6 has provided therein a recess 354 inwhichis positioned one end of the counter-balancing lever 350. Such endof the counter-balancing lever 350 has provided therein a slot 355 forengaging a pin 356 mounted in the recess 354. At the opposite end of thecounter-balancing lever 350 is a weighted member 351 counter-balancingthe switch mechanism and exerting a force upon the switch actuating post2 l 6.

It will thus be seen that upon the switch mechanism through the inertiathereof tending to move the post 2l6 in one direction, the correspondinginertia of the weight 351 will tend to exert through thecounter-balancing lever 350 a force acting in the opposite directionupon the post 2l6. Thus the inertia of the one will counter-balance theinertia of the other and prevent opening of the switch contacts due toswitch mechanism inertia caused by the rapid speed of operation of theaircraft.

I claim as my invention:

1. An instrument for use in an aircraft comprising, in combination, anacceleration responsive device and a control mechanism; said controlmechanism including an actuating member, an aerodynamic conditionresponsive device operatively engaging said member at an intermediatepoint, first and second spring means connected to said member atopposite sides of said point for resisting movement of said member bysaid aerodynamic condition responsive device, and control devicesactuated respectively by opposite ends of said member; said accelerationresponsive device being connected to said control mechanism incounter-balanced relation thereto.

2. An aircraft instrument, comprising, in combination, an elongatedactuating member, a pair of circuit controlling means actuatedselectively by the ends of said member, airspeed responsive meansoperatively engaging said member, biasing means associated with each endof said member for exerting different effects thereon whereby saidcircuit controlling means are actuated at different values of airspeedconditions, 'one'of said controlling means actuated by the actuatingmember when the air-speed responsive means moves the actuating member inone direction at a maximum air-speed value, the other of saidcontrolling means actuated by the actuating member when the air-speedresponsive means moves the actuating member in a second direction at aminimum air-speed value and means for adjusting at leastone of saidbiasing means to vary the condition value at which the correspondingcircuit controlling means is actuated.

3. An instrument for use in an aircraft comprising, in combination, anactuating member, first and second means biasing opposite ends of saidmember in one direction, third means for moving said member in anotherdirection, control devices actuated respectively by opposite ends ofsaid member upon movement of said third means, and fourth biasing meansbeing connected to said member in counter-balanced relation thereto forstabilizing said member against movement by inertia forces.

4. An aircraft instrument for measuring predetermined minimum andmaximum differentials of static and dynamic air pressures, comprising,incombination, means responsive to the differential of static anddynamic air pressures, a lever, a member operated by said means engagingsaid lever at a point intermediate its ends, a first means exerting aforce on said lever on one side of said point for measuring saidpredetermined minimum differential of static and dynamic air pressures,a second means exerting a force on said lever on the other side of saidpoint for measuring said predetermined maximum differential of thestatic and dynamic air pressures, and control means operated by saidlever upon the occurrence of said minimum and maximum differentials ofthe static and dynamic air pressures.

5. An aircraft instrument for measuring predetermined minimum andmaximum differentials of static and dynamic air pressures, comprising,in combination, means responsive to the differential of static anddynamic air pressures, a lever, a member operated by said means engagingsaid lever at a point intermediate its ends, a first means exerting aforce on said'lever on one side of said point for measuring saidpredetermined minimum differential of the static and dynamic airpressures, a second means exerting a force on said lever on the otherside of said point for measuring said predetermined maximum differentialof the static and dynamic air pressures, control means operated by saidlever upon the occurrence of said minimum and maximum differentials ofthe static and dynamic air pressures, and visual indicating meansindicating the amount of the forces exerted on the lever by the firstand second means, whereby the value of the minimum and maximumdifferentials of the static and dynamic air pressures measured by thesaid first and second means may be determined.

6. An aircraft instrument comprising in combination, a casing, adiaphragm movably mounted within said casing, static and dynamicatmosspheric pressure connections leading into said casing fordifferentiallyactuating the diaphragm, a

post mounted on said diaphragm and movable therewith, an elongatedactuating arm operably engaged by said post at a point intermediate theopposite ends of said arm and said post biasing the arm in onedirection, a pair of pivoted bellcrank levers, each of said bell-cranklevers linked at an end to opposite ends of said actuating arm, a pairof springs connected to other ends' of said bell-crank levers in such amanner as to exert biasing forces upon said actuating arm opposite indirection to that in which the actuating arm is biased by the actuatingpost aforesaid, a first pair of electrical switch contacts positioned atone end of the actuating arm and at one side thereof, a second pair ofelectrical switch contacts positioned at the other end of said actuatingarm and at the opposite side thereof, whereby upon the diflerentialpressure exceeding the tension of one of said springs the first pair ofswitch contacts will be actuated to an open position and upon thedifferential pressure decreasing below the tension of the other of saidsprings the second pair of switch contacts will be actuated to an open.

position.

7. An aircraft instrument comprising in combination, a casing, adiaphragm movably mounted within said casing, static and dynamicatmospheric pressure connections leading into said casing fordifferentially actuating the diaphragm, a post mounted on said diaphragmand movable therewith, an elongated actuating arm operably engaged bysaid post at a point intermediate the opposite ends of said arm and saidpost biasing the arm in one direction, a pair of pivoted bellcranklevers, each of said bell-crank levers linked at an end to opposite endsof said actuating arm, a pair of springs connected to other ends of saidbell-crank levers in sucha manner as to exert biasing forces upon saidactuating arm opposite in direction to that in which the actuating armis biased by the actuating post aforesaid, a first pair of electricalswitch contacts'posltioned at one end of the actuating arm and at oneside thereof, a second pair of electrical switch contacts positioned atthe other end of said actuating arm and at the opposite side thereof,whereby upon the differential pressure exceeding the tension of one ofsaid springs the first pair of switch contacts will be actuated to anopen position and upon the differential pressure decreasing below thetension of the other of said springs the second pair of 'switch contactswill be actuated to an open position, and manually operable means foradjusting the tension of said springs, including visual means forindicating the extent of such adjustment of said springs.

8. An aircraft instrument comprising in combination, acasing, a pair ofpressure responsive bellows movably mounted within said casing, staticand dynamic atmospheric pressure connections leading into said casingfor differentially actuating said bellows, a pair of resilient switchblades, a first contact positioned at an end of one of said blades andat one side thereof, and a sure, whereby said switch blades are actuatedrespectively upon predetermined maximum and minimum differentialpressures so as to disengage said contacts.

9. An aircraft instrument comprising, in com-' bination an actuatingarm, means responsive to the differentials of static and dynamic airpressures operably engaging said arm at an intermediate point, firstmeans limiting movement of said arm in one direction at one end of saidarm,

second means limiting movement of said arm in I 19 the oppositedirection at the other end of said arm, and said am so arranged as topivot about said first and second limiting means, first control meansactuated upon pivotal movement of said arm about said first limitingmeans in response to movement of said responsive means in one directionresponsive to a predetermined maximum differential of the static anddynamic air pressures, and second control means actuated upon pivotalmovement of said arm about said second limiting means in response tomovement 01 said responsive means in an opposite direction at apredetermined minimum differential of the static and dynamic airpressures;

10. An aircraft instrument, comprising, in combination, a first controlmeans, a second control means, and means responsive to thedifierentialsof the static and dynamic air pressures, the first of said control meansbeing actuated upon a predetermined maximum difierential of the staticand dynamic air pressures; the second of said control means beingactuated upon a predeter-,

mined minimum difierential of the static and dynamic air pressures,first and second biasing means exerting forces upon said responsivemeans for measuring the difierentials of the static and dynamic airpressures at which said responsive means will actuate said first andsecond control means, and adjustment means for varying the force appliedby said biasing means whereby said maximum and minimum differentials ofstatic and dynamic air pressures may be adjusted.

11. An aircraft instrument, comprisingin combination, a first controlmeans, a second'control means, a responsive means actuated by thedifferential of the static and dynamic air pressures for actuating thefirst of said control means upon a predetermined maximum differential ofthe static and dynamic air pressures and for actuating the second ofsaid control means upon a predetermined minimum difierential of thestatic and dynamic air pressures, means for adjusting the movement inresponse to differentials of the static and dynamic air pressures ofsaid responsive means, whereby said maximum and minimum diiferentials ofthe static and dynamic air pressures may be adjusted.

12. A device of the character described, comprising, in combination, acasing, a pair of actuating bellows movably mounted within said casing,static and dynamic atmospheric pressure conduits, the static pressureconduit leading into the interior of said actuating bellows and thedynamic pressure conduit leading into the interior of the casing in sucha manner as to exert a pressure upon the exterior of said actuatingbellows so that the static and dynamic pressure effect differentiallysaid actuating bellows, each of said actuatthe other oi said actuatingbellows upon a preing bellows including an adjustmentbellows springfastened at one end by said adjustment bel-- lows and said springengaging at the opposite end the inner surface of the free end of saidactuating bellows, a screw-threaded shaft and a nut mounted within saidadjustment bellows, said nut 'screw-threadedly engaged on said shaft andsaid nut afllxed at one end to said adjustment bellows for expanding andcontracting the adjustment belows upon adjustment of the shaft in such amanner as to regulate the tension exerted by said spring upon saidactuating bellows; a, first control means actuated by one of saidactuating bellows upon a predetermined decrease in said difierentialpressure, a second control means actuated by determined increase in saiddifierential pressure. adjustment knobs mounted on each of saidscrewthreaded shafts, and indicator markings for cooperation with saidknobs ior indicating the airspeed at which said first and second controlmeans will be actuated respectively.

13. The combination comprising a first bellows, a-second bellows mountedwithin said first bellows, and spring means operatively engaging saidfirst bellows and said second bellows, a block slidably mounted withinsaid second bellows and aifixed at one end oi. said second bellows, ashaft mounted within said second bellows and screwthreadedly engagingsaid block whereby said second bellows may be expanded and contractedfor adjustment of said spring means, an adjustment knob mounted on saidshaft exteriorly of said second bellows, and indicator means forindicating the adjustment of said spring means.

14. An airspeed responsive device for actuating a switch, comprising, incombination a first switch actuating bellows, a casing enclosing saidfirst bellows, a first conduit for conducting static atmosphericpressure into the interior of said first bellows, a second conduit forconducting dynamic atmospheric pressure into the interior of said casingso as to act upon the exterior of said first bellows, a second bellowsmounted with in said first bellows, a compression spring secured at oneend by said second bellows and operatively engaging at the opposite endsaid first bellows, a block aifixed within said second bellows andattached at the free end of said second bellows, said second bellowsafilxed at the upper end to said casing, a shaft projecting through saidcasing into said second bellows and screw-threadedly engaging saidblock, whereby said bellows may be expanded and contracted foradjustment of said compression spring, an adjustment knob mounted onsaid shaft exteriorly of said casing, and indicator means cooperatingwith said knob for indicating the airspeed at which said first bellowswill actuate said switch.

15. An aircraft instrument, comprising, in com-- 'bination, a, firstswitch blade, a second switch blade, 2. first contact for engagementwith said first switch blade, a second contact for engagement with saidsecond switch blade, a first spring biasing said first switch blade intoengagement with said first contact and a second spring biasing saidsecond switch blade out of engagement with said second contact, controlmeans actuatable in one direction for moving said first switch blade outof engagement'with said first contact, and said control means actuatablein another direction for moving said second switch blade from engagementwith said second contact, and means responsive to the differentials ofstatic and dynamic air pressures for selectively actuating said controlmeans in said directions.

16. An aircraft instrument, comprising, in combination, a first switchblade, a second switch blade, a first contact for engagement with saidfirst switch blade, a second contact for engagement with said secondswitch blade, 9. first spring biasing said first switch blade intoengagement with said first contact and a second spring biasing saidsecond switch blade out of engagement with said second contact, controlmeans actuat able in one direction for moving said first switch bladeout of engagement with said first contact, and said control meansactuatable in another direction for moving said second switch blade outof engagement with said second contact, air- 21 speed responsive meansfor selectively actuating said control means in said directions and aslidably adjustable member engaging one of said springs for adjustingthe spring rate of said one spring.

17. An aircraft instrument, comprising, in combination, a controlmember, an actuating member, means responsive to the differentials ofstatic and dynamic air pressures operably connected to said actuatingmember, spring means for biasing said member for determining the valuesof the differentials of the static and dynamic air pressures at whichsaid member may be actuated by said responsive means, first means foradjusting the spring rate of said spring means, and second means foradjusting the tension of said spring means.

18. In an aircraft instrument for measuring predetermined minimum andmaximum differentials of static and dynamic air pressures, comprising,in combination, means responsive to the differential of the static anddynamic air pressures, means actuated by said responsive means, a firstbiasing means associated with said actuating means for measuring saidpredetermined minimum diiferential of the static and dynamic airpressures, a second biasing means associated with said actuating meansfor measuring said 3 predetermined maximum differential of the staticand dynamic air pressures, and control means actuated by said actuatingmeans upon the occurrence of said minimum and maximum diflerentials ofthe static and dynamic air pressures.

19. In an aircraft instrument, comprising, in combination, a firstswitch blade, a second switch blade, a first contact for engagement withsaid first switch blade, a second contact for engagement with saidsecond switch blade, a first spring biasing said first switch blade intoengagement with said first contact and a second spring biasing the saidsecond switch blade out of engagement with said second contact, anairspeed responsive diaphragm, a post mounted on said diaphragm, alever, said post engaging said lever at a point intermediate theopposite ends of said lever, a first link connecting one end of saidlever with said first switch blade, a second link connecting the otherend of said lever with said second switch blade, the diaphragm actuatingthe lever in one direction through means of said post at a predeterminedhigh airspeed so that the lever through means of the first link movesthe first switch blade out of engagement with the first contact, and thediaphragm actuating the lever in a second direction through means of thepost at a predetermined low airspeed so that the lever through means ofthe second link moves the second switch blade out of engagement withsaid second contact.

20. In an aircraft instrument, comprising, in combination, a firstcontrol means, a second control means, responsive means actuated by thedifierentials of static and dynamic air pressures, the first of saidcontrol means actuated upon a predetermined minimum difierential of thestatic and dynamic air pressures, the second of said control meansactuated upon a predetermined maximum difi'erential of the static anddynamic air pressures, and means for adjusting the movement of saidresponsive means in response to the diflerentials of static and dynamicair pressures so that said minimum and maximum diiierentials of saidstatic and dynamic air pressures may be adjusted.

21. In an aircraft instrument, comprising, in

combination, a first switch blade, a second switch blade, a firstcontact for engagement with said first switch blade, a second contactfor engagement with said second switch blade, 9. first spring biasingsaid first blade into engagement with said first contact and a secondspring biasing said second switch blade out of engagement with saidsecond contact, a control means actuable in one direction for movingsaid first switch blade out of engagement with said first contact, saidcontrol means actuable in another direction for moving said secondswitch blade out of engagement with said second contact, and an airspeedresponsive means for selectively'actuating said control means in saiddirections. 22. In an aircraft instrument, comprising, in combination, afirst switch blade, a second switch blade, a first contact forengagementwith said first switch blade, a second contact for engagement with saidsecond switch blade, a first spring biasing said first blade intoengagement with said first contact and a second spring biasing saidsecond switch blade out of engagement with said second contact, acontrol means actuable in one direction for moving said first switchblade out of engagement with said first contact, said control meansactuable in another direction for moving said second switch blade out ofengagement with said second contact, an airspeed responsive means forselectively actuating said control means in said directions, andslidable adjustable means for engaging the first and second biasingsprings for adjusting the spring rates of said springs.

23. In a control device, a pressure responsive diaphragm operativelyengaging a first lever, a switch actuated by said first lever, aresilient lever hinged to said first lever at one end and abutting saidfirst lever intermediate its length, and means for varying the positionof the remote end of said resilient lever.

24. In a control device, a pressure responsive diaphragm operativelyengaging a, first lever, a

switch actuated by said first lever, a resilient lever hinged to saidfirst lever at one end and abutting said first lever intermediate itslength, means for varying the position of the remote end of saidresilient lever, and means for varying the point of abutment betweensaid first lever and said resilient lever.

ALBERT E. BAAK.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS -Jones Dec. 7, 1943

